Design and Fabrication of Luneburg-Type Waveguide Lenses.

Luneburg-type waveguide lenses are one of the many components used in integrated optical circuits. The imaging characteristics of these lenses are determined by the effective index of refraction. This effective index of refraction depends not only on the physical parameters of the waveguide structure, but also on the polarization, wavelength, and mode number. A waveguide lens can thus suffer from polarization, chromatic, or modal aberration. A four stage design methodology is presented which allows the designer to choose the waveguide thicknesses and indices in an efficient manner to correct the aberrations of the waveguide lens. These lenses are typically fabricated by deposition of a high index of refraction material through a circularly symmetric mask to give a circularly symmetric overlay on the planar dielectric waveguide with a spatially varying thickness profile. They can also be fabricated in a three -layer planar dielectric waveguide by creating a spatially varying index of refraction profile in the guiding layer of the waveguide. Waveguide lenses fabricated in a three -layer waveguide structure are demonstrated via an electron beam lithographic process.